What is the chief ore of mercury?

Cinnabar

The chief ore of mercury is cinnabar \((HgS)\), also known as mercury sulfide. It is a red-colored mineral and the primary source of mercury. Cinnabar is relatively rare and is typically found in hydrothermal veins associated with volcanic and hot spring deposits. Mercury is extracted from cinnabar through a process called roasting, which involves heating the ore to convert the mercury sulfide into mercury vapor, which is then condensed and collected.